The present invention relates generally to controlling the growth of microorganisms. More specifically, the present invention relates to methods for inhibiting the growth of filamentous microorganisms in industrial process waters.
The presence of microorganisms in waters, especially industrial waters, is a never-ending concern for industrial manufacturers. Examples of industrial waters where microorganisms can interfere with industrial processes include cooling tower waters, mining process waters, food processing waters, sugar reprocessing waters, wine and brewery waters and the like.
In particular, the growth of microorganisms in pulp and paper mill waters can adversely affect finished paper products. Paper mills provide extremely good conditions for the growth of microorganisms. The warm temperatures and rich carbohydrate containing fluids of paper machines provide ideal growth conditions for a variety of microorganisms. The contaminating microorganisms are capable of causing spoilage of pulp, furnish, or chemical additives. When deposits break loose and fall into the paper furnish, they result in quality loss or end product defects such as holes and spots. The end result is unsalable paper or paper sold at a lower value. Robertson, The use of phase-contrast microscopy to assess and differentiate the microbial population of a paper mill. TAPPI Journal, p. 83 (March 1993).
The presence of microorganisms within industrial water systems results in the formation of deposits of biological origin on industrial machines. These formation deposits give rise to: corrosion; breaks; increased down time; loss of yield; high chemical costs; odors; and expensive deposit control programs. In the paper mill industry, slime deposits are reportedly responsible for nearly 70% of all breaks, blockages and pump failures. Safade, Tackling the Slime Problem in a Paper-Mill. PTI, p. 280 (September 1988). Slime may be defined as an "accretion or accumulation caused by certain micro-organisms in the presence of pulp fiber, filler, dirt and other materials, mixed in varied proportions, having variable physical characteristics and accumulating at continuous changing rates." Id.
The conventional method of controlling microbial growth is through the use of biocides. Biocides are generally divided into two main groups: oxidizing; and non-oxidizing. These biocides act on the microorganisms in one of three ways: either by attacking the cell wall; the cytoplasmic membrane; or the cellular constituents. Id. at 282.
While biocides do inhibit microbial growth, economic and environmental concerns require improved methods. A problem with the use of biocides is that high levels of expensive chemicals are needed to control microbial growth. Moreover, such chemicals are highly toxic in the quantities known to be required for effective control of microbial populations. As a result, environmental regulations restrict the amount of biocides that can safely be discarded into the environment.
As an alternative to treatment with biocides, researchers posited the use of enzymes to control slime accumulation. U.S. Pat. No. 3,824,184 to Herbert J. Hatcher relates to the addition of levan hydrolase to industrial waters having a slime accumulation or potential slime problem. Similar to using a mixture of various biocides, the use of a multiple enzyme blend to control industrial slime is also known. See U.S. Pat. No. 5,071,765 to Christopher L. Wiatr.
While a biocide or an enzyme alone inhibits slime growth, researchers report that the combination of a biocide and an enzyme together provides even greater benefits. For example, U.S. Pat. No. 4,684,489 to Pederson et al. relates to the combination of a biocide and a polysaccharide-degrading enzyme to reduce slime accumulations. Past combinations focus on using an enzyme, such as levan hydrolase, to degrade the capsule layer around the cell of the microorganism. However, although the combination of the biocide and the levan hydrolase may provide increased control against some sorts of slime growth, it has no affect on sheathed microorganisms.
Conventional treatments fail to recognize the problems caused by filamentous microorganisms in water systems. A group of microorganisms, including the filamentous bacteria, enter industrial systems via the fresh waters. In a typical treatment program, the proper chlorination of waters is always recommended as a means to kill these microorganisms before they enter the system. Unfortunately, proper chlorination is often not a viable option since many filaments have a protective sheath that protects them from anti-microbial agents. While the industrial biocide/enzyme combinations that are presently available work well in killing unsheathed, nonfilamentous bacteria, they fail to limit or reduce the microbial population of filamentous bacteria. In fact, research has shown that 85% of the paper machine deposit samples for alkaline mills currently show filamentous bacteria as one of the major portions of the deposit matrix.
Therefore, a need exists for improved methods for controlling the growth of filamentous microorganisms in industrial process waters.